Intrathecal Atropine to Prevent Nausea and Vomiting After Spinal Anesthesia With Morphine for Elective Caesarean Section: a Randomized Controlled Trial

Intrathecal (IT) morphine grants effective, durable and safe analgesia after Caesarean section. The most common adverse effects after IT morphine are widespread pruritus and postoperative nausea and vomiting (PONV).

Postoperative nausea and vomiting is multifactorial in origin; in addition to general and pre-existing risk factors, such as elevated gonadotropin and progesterone serum levels, parturients undergoing Caesarean section are exposed to drug-induced, hemodynamic and surgical (manipulation of the uterus) stimuli.

Anticholinergic agents, and particularly scopolamine, have long been known to decrease opioid-related nausea and vomiting, although their narrow therapeutic range and inconvenient route of administration (typically transdermal) has limited their application. Anticholinergic agents are thought to act via inhibition of muscarinic receptors in several regions of the medulla oblongata, which are implicated with nausea and vomiting generation; in addition to the chemoceptor trigger zone, these receptors are particularly concentrated in, but not limited to the nucleus tractus solitarius. Cholinergic receptors have been typically associated with motion sickness, but cholinergic agonists such as neostigmine have been shown to increase the incidence of PONV, especially when injected intrathecally.

Anticholinergic agents with muscarinic selectivity may be effective in preventing and treating PONV. Intravenous (IV) administration of scopolamine or atropine, but not glycopyrrolate, reduces the incidence of PONV. Intuitively, as glycopyrrolate does not cross the blood-brain barrier, most postoperative anti-emetic effects of anticholinergic drugs should be mediated by central receptors.

Few studies have specifically evaluated the antiemetic effect of IV atropine after balanced general or opioid-based regional anesthesia, with conflicting results. Atropine may represent a valid alternative to scopolamine and its adverse effects; however, its apparent duration of action is "brief" (minutes to 1 hour) when administered IV.